When you try to run a migration batch job it
fails with "Error: MigrationPermanentException: The target mailbox doesn't
have an SMTP proxy matching "mail.onmicrosoft.com". The target
mailbox doesn't have an SMTP proxy matching" this is because DirSync has not
added the target Office 365 SMTP domain as a proxy address.
If you open the problematic user with Advanced
Features click on Attribute Editor from the Properties window and find the proxyAddresses attribute.
Ensure that there is an SMTP address for your
Office 365 namespace. Ensure SMTP is in lower case or it will be treated as the
primary SMTP address for that user.